1. Field of the Invention
The present invention pertains generally to atomization and drying of liquids, particularly liquids that have a propensity to clog atomization devices, examples include, but are not limited to adhesives, sealants, coatings, and paint. The present invention pertains particularly to devices and methods used in the remote sealing of ducts, more particularly to the remote sealing of ducts used in heating, ventilation, and air conditioning (HVAC) systems, and yet more particularly to duct sealing systems using sealants propelled by heated gas.
2. Description of the Relevant Art
U.S. Pat. No. 5,522,930 (the '930 patent), incorporated herein by reference, discloses a method and device for sealing leaks remotely by means of injecting a previously prepared aerosol into a duct system to be sealed. However, the system uses an external heating source for drying of the diluted aerosols that are sprayed, nominally at room temperature. The aerosols are diluted to reduce particle size by means of evaporation, and thereby improve penetration of the duct system.
U.S. Pat. No. 5,980,984 (the '984 patent), incorporated herein by reference, discloses a method and device for remotely sealing ducts by calculating the particle sizes, and injecting them into a pressurized duct having unsealed leaks. The method of particle size calculation produces particles that have an optimized sealing ability, yet due to their optimized size are best transported by the bulk flow to the site of unsealed leaks. After properly configuring a duct system as outlined in the '984 patent, by determining the change of the duct pressure and flow during the sealing process it can be determined whether the duct has been sufficiently sealed.
Prior nozzles tested for use in duct sealing operations have included those manufactured by Delavan Spray Technologies, Bete: Industrial Spray Nozzles, PNR America, Schlick-Düsen, and Spraying Systems Co., as well as various counter-rotating vortex nozzles. These prior nozzles variously suffered from frequent clogging and/or a particulate spray cone angle too wide for direct injection within narrow ducts.
Narrow ducts form a limiting application for duct sealing applications. In residential homes, and small ducts in commercial systems, ducts may be as narrow as 100 cm. The narrow ducts set a limit to how wide of a spray cone angle may be for these applications. Spray cone angle is more fully developed and described in Atomization and Sprays, by Arthur H. Lefebvre, Hemisphere Publishing Company, 1978, pages 296–301, and are hereby particularly incorporated by reference. The concept relates to the conic shape of spray as it leaves a nozzle, and is typically measured photographically by viewing the included angle of the spray. For most commercial and residential duct sealing applications, the spray cone angle is preferably less than 20°, more preferably less than 15°, and most preferably less than 10°. While these spray angles work well in narrow ducts, they will also work well in wider ducts.
Counter-rotating vortex nozzles do not appear to have serious clogging problems, however they create large spray angles and require considerable dilution (e.g. nine parts liquid to one part solid) to make particles in a size range suitable for sealing ducts. Such large spray cone angles are unusable for sealing narrow ducts, as a large fraction of the overall spray output is immediately coated on the sides of the narrow duct, thereby reducing the availability of downstream sealant particles and thereby increasing sealing time.
Compressed-air nozzles use a propellant gas (typically air, although other gasses may be used), and a liquid feed to create smaller liquid particles, thereby reducing the amount of dilution required to create correctly sized smaller particles. The smaller particles also reduce the quantity of heat required to evaporate the diluent. By concentrating the heat in the propellant gas, heat is delivered more efficiently to the particles, further reducing heating requirements.
When the propellant gas is heated, preferably forming simple heated compressed air, clogging within the atomizer is increased. The present device includes the advantages of heated propellant gas, however mitigates heat-induced clogging by limiting heat transfer to the liquid to be atomized while the liquid is resident within the device.
Both the '930 and '984 patents teach the heating of the bulk gas flow into and through the duct. This heating serves the principal purpose of drying a volatile diluent added to a liquid sealant used for duct sealing. The diluent reduces the size of the sprayed sealant particles that remain after drying or desolvation, thereby producing the appropriate particle sizes required to penetrate and seal duct systems.
Diluting the sealant poses two problems. First, for the sealant to work effectively, the diluent (otherwise referred to as a solvent) must be evaporated so that the particles produced consist essentially of desolvated sealant material. Thus, dilution increases the heat requirements per unit mass of desolvated sealant delivered. This is an important reason for heating the bulk flow gas into and through the duct. Significant electrical power may be required for heating the bulk flow gas depending on the size (volume of the ductwork) and leakage level of the ductwork being sealed, as well as the temperature and humidity of the ambient air being used for sealing. The heated bulk gas flow rate (and thus the heating requirement) is higher for longer (hence higher volume) or leakier ducts, and the heating requirement is also higher for high-humidity or low-temperature ambient air. Second, for a given liquid flow rate, the quantity of desolvated sealant delivered to the ducts is proportionately reduced by the amount of dilution. For common dilutions of one part sealant to nine parts diluent (a ratio of 1:9), sealing can take three times longer as compared to when one part sealant to three parts diluent (a ratio of 1:3) is sprayed, with other factors held constant. More simply stated, for the same liquid flow rate, the sealant mass flow rate is reduced by a factor of three due to the three times higher dilution. The injector and method of using the injector described here reduces the required sealant dilution, and thereby increases the sealant mass flow rate.
Another disadvantage found in current embodiments of both the '930 and '984 patents is the requirement that the ducts be connected to an external fan and spray apparatus, which may be difficult to install, and intrusive in inhabited buildings. In these situations, considerable time and expense may be required simply to gain access to the ducts and isolate the HVAC equipment from the aerosol particles.
The above disadvantages and more are addressed in the present apparatus and method of using the apparatus, yielding a much less intrusive system capable of in-situ duct sealing of previously installed duct systems in occupied commercial and residential buildings. By occupied, we refer to buildings tenanted and in normal use. For previously installed HVAC systems capable of creating sufficient gage air pressure (known in fluid mechanics as “pressure head”, or more simply “head”), no external fan assistance is required to increase the head. This situation is frequently found in commercial structures that have higher-pressure fan systems, and more recently in residential high-pressure HVAC systems. In most homes, there is insufficient head produced to allow effective duct sealing, and an additional fan must be placed in series with, and in addition to, the originally installed fan in order to raise the head sufficiently to seal the ducts. The additional series fan creates sufficient additional differential pressure in the duct system to force sealant particles through existing duct leaks; the particles, in turn, seal the duct leaks. After sealing has been accomplished, the series fan is removed, leaving the original fan system intact. The current injector allows the sealant spray to be created internally within the duct system, thereby simplifying the connection of the external fan to the duct system and the isolation of the HVAC equipment from aerosol particles. Nearly all fan systems have doors for fan access, however the atomizers used by the earlier inventions for duct sealing applications did not allow use of those access doors to connect the external fan, as the aerosol particles were created right at the external fan, and would be blown through the fan and HVAC equipment, thereby unacceptably coating the equipment with sealant. The current injector allows the sealant spray and the external fan to be separated.
The present injector allows for easily patched access to architecturally covered ductwork, allowing for easy placement of compact injectors throughout the building duct system.